Preparation of spinnable solutions of polyacrylonitrile and related polymerisates



Dec. 4, 1956 E. PiROT ET AL 7 PREPARATION OF SPINNABLE sowrxous 0F POLYACRYLONITRILE AND RELATED PQLYMERISAT ES Filed Nov. 17, 1954 firronmsr Unite States Patent PREP+2ARATI0N F SPINNABLE SOLUTIONS or PQLXACRYLONITRIILE AND RELATED POLY- MERISATES Ernst Biriitg- Erlenbach (Main), and Eduard Hantelmann,

Aachen, Germany assignors1o Vereinigte Glauzstotf- Fabrlkeu' A. G.,- Wuppertal- Elberfeld, Germany, a corporationofrGei-lnany Application Nove'mbern, 1954, Serial No. 469,495

Claims priority, application Germany November 21, 1953 2 Claims. c1. 260 -325 This invention relates to the preparation of a solution ofpolyacrylonitrile or the mixed polymerisates thereof forthe purpose of'spinning the same. In' particular it is directed to 'the preparation of a solution which, after usual filtratiomcanbe spun'without diflic'ulty into threads with good textile properties.

The manufacture of solutions"froin polyacrylonitrile or itsmixed polymerisates having good spinning properties has been'very dilficult; For instance, the quality of the' spinningsolution' is appreciably efiected, among others,'by application of a definite temperature and by the use of a polymerisate having a definite particle size. If, for "example'jthe polymerisate consists of coarse particles, jorif a definite temperature is not maintained during the preparation of the dispersion andthe solution formed'therefrom,'or if the heating is carried out too rapidly or too longo'r non uniforin'ly, and the dispersion is not vigorously stirred during heating, then under such conditions spinning solutions are formed from which only threads of inferio'rquality c'an'be spun. The effort' of many-previously conducted investigations was in the direction of eliminating, as much as possible, known sources of defects by resort to special steps. For example, it has been heretofore proposed to use for the preparation of polyacrylonitrile spinning solutions such high polymers which have a particle size of about 100 mu or less. Such extremely finely pulverized high polymers are then dispersed in known solvents, as for example, dimethylformamide at low temperatures, then vigorously stirred and the temperature of the dispersion gradually elevated to about 120 until a spinning solution is formed. It has also been proposed to apply a vacuum during the formation of the dispersion at low temperatures for the purpose of simultaneously deaerating the spinning solution. According to still other proposals, the dispersion is prepared at temperatures below freezing, that is, at temperatures of about 5 to 20 C., and subsequently converting the same into spinnable solutions by rapid heating. According to a further proposal, very finely pulverized polymerisates are injected, by means of an inert gas current, as for example, by means of a current of nitrogen into a reaction vessel through a nozzle while the solvent is simultaneously fed into the reaction vessel. The dispersion which is formed is then heated to temperatures up to 100 C., and the resulting spinning solution is spun by conventional methods.

' The aforedescribed methods illustrate the difliculties which are encountered in manufacturing spinnable solutions of polyacrylonitrile. However, even if those previously proposed conditions are maintained, the resulting solutions do not always assure the spinning of threads having good textile properties.

It has now been discovered that by maintaining conditions in accordance with this invention, good spinning solutions of polyacrylonitrile or its mixed polymerisates are obtained from which threads with excellent textile properties mayfbe produced." In carrying 'out this invention'a specifically designed vacuumvessel which has a temperature gradient is used'for the manufacture of the spinning solution. This temperature gradient is obtained by means'ora novel'he'a'ting jacket for the vacuum-vessel.

Theheatingljacketenvelopes the vacuum vessel in such wise that the upper and the lower part of the vacuum vessel are not covered by the jacket.

the vacuum" vessel are 'most'vigorously heated by-a suitableelectric heating device, whereas the heating continuou'sly diminishes toward' the upper and the lower parts of the vacuum vessel. This resultsin the heating gradient required for carrying out themiethod in accordance with thisinvention. An additional step forcarrying out the instant method is that of introducing a freshly prepared" reactionvessel. -The dispersion within the reaction vesselis continuously stirredby suitable mechanical means.

Due tothe efEect of the heating jacket, the temperature of the dispersion in the vacuum vessel may be elevated to about to C. By adjustment to a selected temperature and simultaneously to a selected vacuum, very vigorous boiling of the solution in the vacuum vessel is initiated and thereby maintained. This step of very vigorous" ebullition is of very great importance in carrying out the method of the invention. The efiect of the strong ebullition to'produce; vigorous agitation of the entire solution whereby rapid and complete dissolution of the very finely pulverized and distributed particles is attained. The surface of the-solution, obviously, will be enriched with ;thesolvent, as for'example dimethylformamide, and in thefree-space of the vacuum vessel above the liquid, a layer of--vap'or of the solvent willbe formed. A refiux condenser serves continuously to condense the excess of the vapor, causing the condensed solvent, as for example dimethylformamide, to flow back onto the surface of the solution. The effect of this step is to prevent the formation of films or skins on the surface of the solution which would interfere with the homogeneity of the spinning solution. The agitator and pump are preferably provided with double glands and a suction jacket to prevent the ingress of air into the vacuum vessel during the preparation of the spinning solution.

In the single figure of theaccompanying drawing a suitable installation for preparing the solution according to the invention is shown by way of illustration and not by way of limitation.

The installation as illustrated comprises a vacuum vessel 1, an agitator 2 with several arms, a feed hopper 3 for simultaneously charging the vessel with polymerisate and solvent, a heating jacket 4 for producing the required temperature gradient, a condenser 5, a vacuum pump 6, a pump 7, that delivers the solution to the spinning site, and filter 8 through which the solution is passed on its way to spinning site 9.

The manner in which the method of this invention is carried out will now be explained in greater detail.

The vacuum vessel is charged with a freshly prepared dispersion consisting of very finely pulverized polyacrylonitrile or its mixed polymerisates and a solvent, for instance, dimethylformamide. The vessel is filled with the dispersion to an extent such that only a small space remains in which a vapor phase can be formed, the level of the dispersion being slightly higher than the upper level of the heating jacket. The vacuum vessel is first heated to a temperature of 100 C. and after having reached this temperature, it is charged with the still cold dispersion through hopper 3. Simultaneously, the spin- Patented Dec. 4, 1956- The mid-section of theheating'jacket and hence, also the mid-section of ning solution after passing through the filter 8 under force of pump 7 is delivered to the spinning location 9 so that a continual operation is initiated and assured. Then, fresh dispersion is added to the vacuum vessel at the rate at which the spinning solution is being continuously delivered to the spinning location.

The method in accordance with this invention can be carried out under the optimum conditions when, during the heating, a vacuum of preferably 100 to 200 mm. Hg and a temperature of preferably 90 to 110 C. are maintained. Suitable solvents having a boiling point of 100 C. or above are typified by dimethylformamide, dimethylacetamide, glycolic acid nitrile, ethylenecarbonate and similar solvents, as well as mixtures of solvents, such as for instance, a mixture of dimethylformamide and methyleneglycoldiacetate.

Example A vacuum vessel, as illustrated, and having a capacity of 15 liters is filled with 10 liters of a dispersion consisting of polyacrylonitrile and dimethylformamide formed by mixing 22% of very finely pulverized polyacrylonitrile and 78% of dimethylformamide. The vessel is heated and simultaneously evacuated. At a temperature of 95 C. and at a vacuum of 100 mm. Hg, the solvent begins vigorously to boil so that the free space in the vacuum vessel above the liquid level is filled with dimethylformamide vapors which are continuously condensed by the reflux condenser 5, disposed above the vacuum vessel, and the condensed dimethylformamide is returned. The strongly boiling solution is vigorously stirred by the agitator 2. A built-in thermometer and a constant vacuum control device are preferably provided to permit control of the dissolving step. As soon as the solution begins vigorously to boil the continuous input of the dispersion through hopper 3 and the simultaneous withdrawal of the finished spinning solution through pump 7 are initiated. The rate of charging the vessel with the dispersion consisting of 22% of polyacrylonitrile and 78% of dimethylformamide is regulated in accordance with the rate that the solution is withdrawn for spinning. In about one hour pump 7 pumps about 10 liters of spinning solution to the spinning site 9 and a corresponding quantity of dispersion is fed into the vacuum vessel through hopper 3. Hence the dispersion and the spinning solution produced therefrom dwell in the vacuum vessel for a period of one hour only. During this period the dispersion is converted into a solution which is free of gelatinous inclusions, is homogeneous and is deaerated. Such a solution makes it possible to produce threads having excellent textile properties.

It will be understood that the foregoing description of the invention and the examples set forth are merely illustrative of the principles thereof. Accordingly, the appended claims are to be construed as defining the invention within the full spirit and scope thereof.

We claim:

1. Method of preparing a solution of polyacrylonitrile for spinning which comprises maintaining a solution of polyacrylonitrile in dimethylformamide in the boiling state under reflux at a pressure of 100 mm. Hg, continuously introducing a stream of a cold dispersion of polyacrylonitrile in dimethylformamide and simultaneously withdrawing andfiltering the same to obtain a filtrate for spinning.

2. Process of preparing a solution of polyacrylonitrile for spinning which comprises maintaining a solution of polyacrylonitrile in a solvent having a normal boiling point of at least 100 C. in the boiling state at an approximate temperature of from 90 C. to 110 C. and under an approximate subatmospheric pressure of from 100 mm. to 200 mm. Hg, continuously introducing into said boiling solution a cold dispersion of the polyacrylonitrile in the said solvent and simultaneously with-' drawing an equivalent stream of the boiling solution, and filtering the same to obtain a filtrate for spinning.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,713 Houtz July 23, 1946 

1. METHOD OF PREPARING A SOLUTION OF POLYACRYLONITRILE FOR SPINNING WHICH COMPRISES MAINTAINING A SOLUTION OF POLYACRYLONITRILE IN DIMETHYLFORMAMIDE IN THE BOILING STATE UNDER REFLUX AT A PRESSURE OF 100 MM. HG, CONTINUOUSLY INTRODUCING A STREAM OF A COLD DISPERSION OF POLYACRYLONITRILE IN DIMETHYLFORMAMIDE AND SIMULTANEOUSLY WITHDRAWING AND FILTERING THE SAME TO OBTAIN A FILTRATE FOR SPINNING. 